in this image it is written Michael Nicolaevitch perhaps but it is an error? the seated man to right , in uniform, is perhaps Nikolai Mikhailovitch ? and the man seated on the left ? the photo is of 1901 in Varna . thanks

That could be one of GD Mikhail Pavlovitch's daughters...but in 1848 only Ekaterina was alive. And the girl doesn't resemble her at all.

Your guess about Alexandra I. sounds quite possible. I see a slight resemblance to her..ahh, if we only had a photo or dagerrotype of Alexandra in the end of 1840s...The portraits with uncertain identity are always like that: "now you see, and now you don't"..)) somewhat "catch me if you can".